The present invention relates to protecting the edge of bonded semiconductor wafers and, more particularly, relates to protecting the edge of a stack of bonded semiconductor wafers during wafer thinning.
In one possible scheme for wafer-scale bonding three-dimension (3D) integration, the top wafer may be bonded face down to the bottom wafer. In general, wafer-scale bonding may be face-to-face bonding or face-to-back bonding. Subsequently, the top wafer is ground and polished from the back in order to leave a relatively thin portion of the top wafer, so that the through-silicon via definition that will facilitate electrical connection is possible. However, grinding mechanically the top wafer to a very small thickness can be very risky and can yield to several process yield issues, such as chipping or cracking, and uniformity issues regarding the remaining wafer thickness. In one possible approach to circumvent this issue, the final wafer thinning step can be done by use of a wet thinning process and thickness and uniformity of the remaining silicon can be influenced by appropriate material selection. However, the wet thinning process is also known to attack dielectric films and carrier wafer surfaces as well.